1. Field of the Invention
The present invention relates generally to agricultural irrigation systems. More particularly, the invention concerns a novel irrigation system and its method of use that permits the agricultural grower to irrigate growing crops with water at an elevated temperature for purposes of freeze prevention.
2. Discussion of the Prior Art
Crop losses due to freeze can exceed millions of dollars per year in the United States alone. For example, in an article published by the San Francisco Chronicle on Wednesday, Jan. 17, 2007, recent losses of the California orange crop due to freezing conditions were estimated to exceed $1 million. These losses occurred even though many growers attempted to protect their crops through the use of wind machines and other types of preventative measures. The estimated cost for operating the wind machines were estimated to be on the order of $200 per hour of operation.
Numerous types of crops, other than oranges, are susceptible to freeze damage. For example, losses by avocado growers in California as a result of the January 2007 freezing conditions were also estimated to be an access of $1 million. Similarly, growing crops such as strawberries, tomatoes, beans, cucumbers, peppers and squash as well as vine crops and tree fruits are susceptible to substantial damage due to freezing.
The critical temperatures needed for damage to occur to growing crops varies depending on the duration that temperatures remain below freezing. For example, buds of fruit trees may be damaged if exposed to −2° C. for more than 24 hours, but may survive if exposed to −6° C. for less than 2 hours. Thawing conditions often affect the extent of damage after a frost. For example, tobacco leaves which are thawed out gradually after freezing have been known to suffer less damage than if thawing was rapid.
Various methods are currently in use by agricultural growers to protect their crops from freeze damage. The more common of these methods include the use of wind machines, the use of smudge pots, controlled irrigation at the onset of the freeze and crop covering.
With respect to the use of wind machines, it is well understood that during freezes that occur on calm, clear nights, the air layer near the ground is colder than the air aloft. With this in mind, wind machines or helicopters are sometimes used to bring the warmer air down to the crop level to replace the cold air layer at the surface. This method can be effective when there are large temperature differences between air layers near the surface and those up higher. However, as previously mentioned, equipment and operating costs are high. Effectiveness varies in the range of 1 to 4 degrees C.
With respect to the use of controlled irrigation, smudge pots and the like, smoke clouds are well-known for their ability to reduce radiative heat loss from the surface. Smoke from smudge pots or burning tires or refuse and mist from fine water nozzles have been used in attempts to reduce this heat loss. Since it is difficult to maintain the smoke over the sensitive crop area and to produce droplets the optimum size to intercept the long-wave radiation, this method is not particularly effective. In addition, in many regions environmental laws prohibit the use of methods where smoke is involved.
Covering methods reduces heat loss from the surface. However, the cost of the covering materials, such as sheets of plastic and the like, their storage and the time and labor needed to place the covers over the growing crop are the main drawbacks to this method particularly for large areas of crops. Foams have also been used experimentally to protect plants but materials and applicators are not readily available on a commercial basis. Sprinkling of the crop normally begins with the onset of freezing conditions and a film of water is attempted to be continuously maintained until temperatures have risen above the freezing level (0° C.). If sprinkling is discontinued prematurely, heat will be drawn from leaves to melt the ice and freeze damage may result. If the frost lasts too long, this method can prove quite detrimental because the plants can only support a limited amount of the added weight of ice that builds up on the leaves and branches.
It is the foregoing deficiencies of the various prior art agricultural crop freeze control methods described in the preceding paragraphs that the present invention seeks to overcome.